I found this article useful too. It is a review of a study...

“As humans are social animals, it’s important for humans to understand the emotional state of other people to maintain good relationships,” says Akihiro Tanaka of Waseda Institute for Advanced Study in Japan. “When a man is smiling, probably he is happy, and when he is crying, probably he’s sad.” Most of the research on understanding the emotional state of others has been done on facial expression; Tanaka and his colleagues in Japan and the Netherlands wanted to know how vocal tone and facial expressions work together to give you a sense of someone else’s emotion.”